1. Field of Invention
The present invention relates to a method for preparing an electrical contact material in a field of materials technology, and more particularly to a method of preparing a fibrous silver-based electrical contact material.
2. Description of Related Arts
With the rapid development of the electrical apparatus industry, the application of electrical apparatus switches has brought about increasingly high requirements on the performance of the electrical contact materials such as high resistance to welding and arc erosion and good conductivity. With regard to these requirements, worldwide researchers have made great efforts to improve the performance mainly by designing material composition and reinforcing particles dispersion uniformity. Compared to the silver-based composite material dispersion-reinforced by ordinary particles, the silver-based composite material reinforced by fiber-like arranged particles has better resistance to welding and arc erosion and a good processing property. The development of a simple and practical method which could be applied to large-scale production has attracted tremendous research interest and still remains to be a difficult point in the present research.
Some researches on silver-based electrical contact materials with fiber-like arrangement of reinforcing nanoparticles are stated as follows.                (a) Yonggen Wang, & etc., Study on the process of the fibrous AgNi composite wire, electrical engineering materials, Vol. 20, No. 1, 2007;        (b) Chinese patent, fibrous structure silver-based electrical contact material and preparation method thereof, having an application number of 200910196283.0 and a publication number of CN101707145A.        
Three traditional methods of preparing silver-based electrical contact materials are as follows. The first is a method of conventional powder metallurgy sintering and extrusion, whose main process includes powder mixing, pressing, sintering, extruding, drawing, annealing, drawing and finally obtaining finished products. This method is unable to obtain the desired neat fibrous structure and may produce large reinforcing particles that severely undermine the performance of the products. The second is a modification of the first method with improved extrusion and increased processing deformation as recited in the research (a). This method is unable to provide fibrous silver-based materials when the processing deformation is small, such as extruding into strips or sheets. Furthermore, this method is not suitable for reinforcing phase with poor plasticity and ductility, such as SnO2. The third refers to a combination of a pre-design of green body and an extruding method. More precisely, a certain number of reinforcing wires are fixed into a matrix through a mould in advance and subjected to isostatic pressing, sintering and extruding as recited in research (b). Although able to create neat and continuous fibrous structure, the third method is not applied to industrial-scale production because the third method is relatively complex and places particular requirement on the plasticity and ductility of the reinforcing wires. In addition, the third method requires that the silver-based wires with reinforcing materials be prepared in advance and fixed into the matrix through the mould. Therefore, it is understood that fibrous silver-based electrical contact materials cannot be obtained either by simple powder mixing or in the situation where the deformation is relatively small or where the reinforcing phase has poor plasticity and ductility.